1. Field of the Invention
This invention relates to a vibration controlling apparatus for buildings which reduces the swinging in the building of a flexible structure system such as high-rise building, tower or the like due to earthquake, wind or the like.
2. Related Art Statement
In the high buildings such as high-rise buildings, various towers and the like, there is adopted a flexible structure system for absorbing vibration energy to increase the earthquake proof strength.
In this flexible structure system, however, the swinging not only is caused at strong wind or earthquake but also becomes large even at normal wind, so that the living comfortability may be reduced.
As a means for reducing the vibration amplitude at normal wind to improve the living comfortability and at the same time reducing the deformation of the building as a whole even at strong wind or earthquake, therefore, it has been proposed to arrange a dynamic vibration reducer (i.e. dynamic damper) for the generation of vibration counteracting the swinging of the building, which comprises a combination of a main spring system consisting of the building itself and an auxiliary spring system connected to the building through a spring and provided with an additional mass and is set so that the natural frequency (vibration period) is approximately equal between the main spring system and the auxiliary spring system to realize the vibration absorbing effect. FIG. 13 shows a structure of this type of the conventional dynamic vibration reducer.
As shown in FIG. 13, a lower part mass 33 movable along a pair of rails 32 horizontally placed on a building 31 (e.g. a top of a tower or the like) in a given direction (Y-direction) and an upper part mass 35 movable along a pair of rails 34 horizontally placed on the lower part mass 33 in a given direction (X-direction) are supported by spring members (not shown) such as spring and the like extending in the Y-direction and X-direction, respectively. Further, each of these masses 33, 35 is slidably supported by a roll having a small friction coefficient, respectively.
Thus, the conventional dynamic vibration reducer for the building is a two-dimensional apparatus, wherein the dynamic vibration reducing effect to the vibration (swinging) of the building 31 in the Y-direction is obtained by the auxiliary spring system consisting of springs of the Y-direction and the upper part mass 35 and lower part mass 33, and the dynamic vibration reducing effect to the vibration (swinging) in the X-direction is obtained by the auxiliary spring system consisting of springs of the X-direction and the upper part mass 35.
In the conventional vibration controlling apparatus for buildings, however, the main spring system and auxiliary spring system having substantially the same vibration period are merely connected to each other (passive damper), so that if it is intended to make the vibration controlling effect large, the mass ratio of the building 31 to additional masses 33, 35 becomes large (in a direction approaching to 1.0) and consequently it is required to increase the strength of the building 31 and the like, which is difficult to be practically realized.
Since the conventional vibration controlling apparatus is a passive damper as mentioned above, the vibration response ratio is determined by the masses 33, 35, spring constant and vibration damping coefficient of the dynamic vibration reducer (auxiliary spring system). As a result, this apparatus has a large effect for particular vibration frequency component, but can not expect the vibration reducing effect against vibrations of wide frequency band such as random vibration and the like.
Further, each of the masses 33, 35 is supported by a roll bearing or the like, so that the static friction coefficient is large in the vibration reducing operation and consequently only the reducing effect against large external force is obtained and the effect to minute vibration can not be obtained.